The present invention relates to an injection assembly for a plastics material injection mould, and for a process for producing an assembly of this type.
More particularly, the invention relates to an injection assembly for a plastics material injection mould, comprising:
heating nozzles for injecting the plastics material into the mould; PA1 these nozzles being supplied with plastics material by at least one central nozzle, from the barrel extruder; PA1 means for controlling the nozzles and for heating the supply ducts of the nozzles; PA1 this injection assembly being intended to be mounted on the matrix of the injection mould. PA1 a bearing plate bearing a heating distributer provided with injection nozzles; PA1 A--the bearing plate is a cast iron or moulded steel part provided with reinforcing ribs and a reserved space for accommodating the heating distributor, and positioning supports for the heating distributor; PA1 B--the heating distributor is a part forming an assembly of heating ducts connected to at least one plastics material input point (central nozzle) and to injection nozzles comprising; PA1 an impression of the distributor, consisting of modular elements for the connectors and branches connecting the connectors is produced; PA1 the elements of the connectors are positioned according to the locations provided for the nozzles; PA1 the connection branches, which have been cut out, are positioned in a profiled section and the junctions between the cores and the connection branches are covered to obtain continuity of the transitory faces; PA1 the mould is produced using the impression of the distributor; PA1 the steel is cast; PA1 the ducts, the apertures of the nozzles and the reference faces of the connectors are machined; PA1 the nozzles and the armoured and closed electrical resistances are positioned in the distributor; PA1 the distributor, thus equipped, is mounted on the bearing plate which is produced separately, of cast iron or moulded steel; and PA1 the supply means of the bearing plate are connected to the distributor.
At present, for the injection of large-scale parts in plastics material, for example those intended for the automobile industry, the injection mould is equipped with an injection assembly comprising heating nozzles to allow the plastics material to be injected, simultaneously, at different locations on the mould in order to ensure a rapid and very uniform distribution of the plastics material inside the mould, a condition which is indispensable for the manufacture of large-scale parts with good mechanical and aesthetic properties.
This injection assembly is currently produced by machining a forged steel block, in which there are provided passages for accommodating the nozzles, the supply ducts of the nozzles and the ducts for supplying the control fluid for the nozzle valves, for heat-exchanging fluid, or for electric supply cables to pass through.
These machining operations are extremely long because it is necessary to remove a significant part of the material; these operations are also very delicate and the injection assembly is not always satisfactory as regards the distribution of heat, the uniformity of the temperature inside the assembly, etc.